The present invention relates to oil well downhole safety valves and more particularly to a downhole safety valve wherein opposing pistons of differing surface areas connected by a passive connector and preferably balanced with a spring are used to seal the well when certain predetermined pressure characteristics are experienced in the well.
Even more partiuclarly, the present invention relates to a downhole safety valve device operable by annular pressure which can be used to operate various downhole tools and to perform various downhole functions including drill stem testing, storm choking, downhole valving, and the like.
In the drilling of oil and gas wells, it is common to use an elongated tubular member which is known in the industry as the casing. The bore of the well inside the casing is known as the well annulus. Frequently, a drill or work drill or production string is placed in the annulus and carries down into the well bore any of a number of downhole tools which are used to perform any of a number of functions in the well bore. Some tools are used as part of the drill stem to test the stem for leaks. Oftentimes, the work or tubing string carries a control or safety valve which protects against blowouts or loss of control of the well. The function of such a control or safety valve is to prevent flow upwardly through the tubing string after the valve closes. The use of a safety valve for the purpose of preventing uncontrolled flow from a well through a production tubing is a common procedure. Numerous patents have been issued for downhole safety valves and downhole ball valves which are directed to a solution of the problem of preventing undesired flow from the well. Examples of downhole safety valves which have been patented include the Mott U.S. Pat. No. 3,844,346, the Deaton et al. U.S. Pat. No. 4,214,606, the Roberts U.S. Pat. No. 4,325,434, and the Vinzant et al. U.S. Pat. No. 4,461,353.
The Mott U.S. Pat. No. 3,844,346, entitled "Subsurface Safety Valve Well Tool Operable By Differential Annular Pressure" describes a well tool apparatus that is adapted for connection in a production tubing. The tool includes a separable flow housing having a bore extending therethrough with a rotatable ball bore closure positioned in the bore which is operable in response to differential fluid pressure in an annular area about the tubing.
The Deaton et al. U.S. Pat. No. 4,214,606, entitled "Subsurface Safety Valve" provides a valve assembly for connection in a well pipe, including a valve member disposed in a valve body having a bore or passageway therethrough, a pair of spaced apart and oppositely facing valve seats in surrounding relation to an intermediate portion of the passageway, the valve positioned thereat and operably to open and close the passageway, a space within the valve body outwardly of the passage therethrough, a control frame guidably movable within the space and having a piston associated therewith adapted to define first and second variable capacity pressure chambers within the space. The control frame in movable is opposite longitudinal directions to open and close the valve. Such movement is perfected by using first and second ports, the first port providing fluid communication between the first variable capacity pressure chamber and an external source of pressure fluid. The second port provides fluid communication between the second variable capacity pressure chamber and the passageway through the valve body.
The Roberts U.S. Pat. No. 4,325,434 entitled "Tubing Shutoff Valve" describes a subsea test valve system for a well completed at the floor of the sea and includes a safety valve and a disconnect mechanism mounted in a blowout preventor at the bottom of the sea and having hydraulic fluid operated means for opening the safety valve and controlling a latch in the disconnect system. Subsea hydraulic pressure operated devices are supplied with pressure fluid from a subsea accumulator under the control of subsea pilot valves which are operated by small pressure differences, to accomplish rapid operation at great depth from a control console on a vessel or platform.
The Vinzant et al. U.S. Pat. No. 4,461,353 entitled "Well Safety Valve" describes a safety valve including a ball valve in the central flow passage of the tool body for controlling pumped fluid flow therethrough.
Haliburton Services of Duncan, Okla. has used a subsurface safety valve which is pressure operated. The device is run in the hole and activated upon reaching a desired position by pressure. The Haliburton apparatus used a safety valve which is a sliding valve construction utilizing annulus hydraulic pressure against a chamber of nitrogen to open the tool. This pressure must be maintained to keep the tool open, and reduction of annulus pressure causes the valve to close. An additional feature of the Haliburton device provides for a closure of the valve into a locked closed position if excessive annulus pressure develops while the tool is open. Normally the Haliburton safety valve is located in the test tool string above a packer. The device is actuated with a predetermined pump pressure which is applied to the annulus fluid. Releasing the pump pressure causes the tool to close.
A downhole safety gate valve is shown in U.S. Pat. No. 4,520,994 entitled "Sub-Surface Safety Gate Valve."That patent describes a valve with an elongated body which is generally cylindrical and providing a longitudinally running flow conveying bore. A valve gate is removable within the confines of the valve body between open flow and closed flow positions and includes at least one gear receptive toothed rack. A gear structure rotatably mounted within the valve body engages the toothed rack and moves the toothed rack of the valve gate between open flow and closed flow positions. An operator shaft, carried by and movable within the confines of the elongated valve body, is provided for engagedly rotating the gear structure. A hydraulic attachment on the valve body allows a controlled hydraulic pressure source to move the operator shafts relative to the valve body. As a failsafe closure of the valve structure, the valve is biased to a closed flow position by providing shafts of varying diameters having a smaller cross-sectional size at one end so that if well pressure leaks into the drive chamber and into the space adjacent the shafts, the pressure acts on the shafts of varying diameter to bias the shaft movement toward the closed flow position.